When Pre-Main Sequence stars have two spectral types, an earlier one measured in the optical and a later one in the IR, the hotter one implies a greater Hertzsprung–Russell Diagram (HRD) mass than the cooler one. The mass discrepancy may be removed by plotting the stars on a modified HRD showing log (Luminosity) versus log (surface gravity). Placing two Pre-Main Sequence stars in Taurus, BP Tau and T Tau N, on such a HRD-like diagram shows that the hotter effective temperature represents the stars’ intrinsic parameter determined by their luminosity and radius and resolves the mass discrepancy in favor of the larger mass.

中文翻译：

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主序列前恒星的类似HRD的图

当“主序前”恒星具有两种光谱类型时，较早的一种在光学上进行测量，而较晚的一种在红外中进行测量，则较热的一种意味着比较冷的一种更大的赫兹—拉塞尔图（HRD）质量。可以通过在修改后的HRD上绘制星图（显示对数（光度）与对数（表面重力））来消除质量差异。在类似HRD的图表上将两颗主前序列恒星放在BP Tau和T Tau N的金牛座中，表明较热的有效温度代表由恒星的亮度和半径决定的恒星固有参数，并解决了质量差异，有利于较大的质量。